1. Field of the Invention
The present invention relates to piezoelectric devices, and in particular relates to a piezoelectric device having piezoelectric elements using a piezoelectric substrate and a piezoelectric thin film, such as a resonator and a filter.
2. Description of the Related Art
Recently, a chip-size package (CSP) has been developed in which a piezoelectric device, such as a surface acoustic wave filter (SAW filter) including a piezoelectric substrate and a bulk-acoustic-wave filter (BAW filter) including a piezoelectric thin film, is miniaturized to an element chip size.
For example, a piezoelectric device 2 shown in FIG. 5 includes a piezoelectric substrate 3 having piezoelectric elements including IDTs (interdigital transducers, interdigital electrodes) 4a and an electrically conductive pattern, such as pads 4b, provided on one principal surface 3a of the piezoelectric substrate 3, a cover 6 covering the one principal surface 3a with a support layer 5 therebetween, and external electrodes 7 which are exposed outside the cover 6. The piezoelectric device 2 is mounted in a face down orientation at a predetermined position of a wiring pattern 1a of a circuit board 1 (see Japanese Unexamined Patent Application Publication No. H11-251866, for example).
The piezoelectric device 2 disclosed in Japanese Unexamined Patent Application Publication No. H11-251866 electrically connects the external electrodes 7 to the pads 4b by forming holes in the cover 6 so as to be embedded with the external electrodes 7 by electrolytic plating or evaporation. Accordingly, since the vibratory space around the IDT 4a cannot be sufficiently sealed, it has been necessary to seal the piezoelectric device 2 by covering it with a reinforcing resin 9 with a buffer resin 8 therebetween after mounting the piezoelectric device 2 on the circuit board 1.